From the state of art electronic and mechanical pipettes with adjustable volume of aspirated liquid are known, which are built in the upper part of a handle and in the lower part of a nozzle terminated with a cone for an exchangeable tip as well as of coupled with them and cooperating with one another mechanisms which realize different functions in the pipette.
An exchangeable pipette tip ejection mechanism comprises an ejector push button seated in the upper part of the pipette handle and an ejector seated with its lower end onto the pipette nozzle.
A drawing up and discharging mechanism comprises a pipetting push button connected via a pipetting rod to a piston assembly of which the plunger is placed in the pipette nozzle and is slidable therein in PIPETTING MODE of the pipette from and to its upper position. The plunger is driven towards the exchangeable tip by force which is manually applied by an user to the pipetting push button. In the opposite direction, the plunger is driven in PIPETTING MODE by the force of the pipetting spring until it rests on an end stop mounted in a plunger working stroke adjustment mechanism.
In ADJUSTMENT MODE, a position of an upper limiter of the plunger working stroke is changed by means of an adjustment screw of the drive assembly of the plunger working stroke adjustment mechanism. The drive assembly of the plunger working stroke adjustment mechanism has at least one driving member which is accessible for the user from outside through at least one window in a wall of the handle. The plunger working stroke adjustment mechanism controls a length of a plunger movement that is performed during liquid pipetting in PIPETTING MODE.
The plunger working stroke adjustment mechanism is via an engaging mechanism engaged with a counter to indicate the volume of the liquid aspirated by the pipette in PIPETTING MODE into the exchangeable tip, whereas the liquid volume is previously set by the user in ADJUSTMENT MODE by selection of a setting of the plunger working stroke.
Thus, the length of the plunger movement that is its working stroke in the nozzle during pipetting in PIPETTING MODE is altered by the user due to resetting structure elements of the plunger working stroke adjustment mechanism in ADJUSTMENT MODE, which simultaneously results in a change of indications of the counter indicating the set and desired liquid volume.
The pipettes are further provided with a calibration mechanism which enables, in CALIBRATION MODE of the pipette, the change in a calibration coefficient of the pipette. The calibration coefficient determines a relationship between the plunger movement length set by the plunger working stroke adjustment mechanism and the liquid volume indicated by the counter.
For ensuring an easy adjustment of the desired volume value of the drawn-up liquid, in the course of resetting adjustment elements of the plunger working stroke adjustment mechanism in ADJUSTMENT MODE, a torque, which is indispensable for setting change, should be as small as possible. Whereas, after adjustment of the desired volume value during operation with the pipette in PIPETTING MODE, this torque should be sufficiently large to rule out any risk of accidental resetting the pipette to another volume value. This requires to apply in the pipette an additional mechanism for changing a braking torque exerted onto the plunger working stroke adjustment mechanism or an additional mechanism for disengaging external adjustment elements of the plunger working stroke adjustment mechanism from elements changing the end stop position which determines the length of the plunger working stroke.
Therefore, for securing the desired volume value of the drawn-up liquid, which is previously set in ADJUSTMENT MODE, against accidental resetting during operation with the pipette in PIPETTING MODE, the pipettes are provided with a manually actuated lock mechanism locking the adjustment mechanism of the plunger working stroke.
In the known pipettes, the lock mechanism of the plunger working stroke adjustment mechanism, which constitutes a releasable friction brake, is more often applied. This lock mechanism provides after its actuation the large braking torque exerted onto the plunger working stroke adjustment mechanism and preventing from unintentional resetting in PIPETTING MODE the set desired volume value of the liquid aspirated by the pipette and simultaneously provides after its releasing the small braking torque exerted onto the plunger working stroke adjustment mechanism and necessary for adjusting the desired volume value of drawn-up liquid.
From the United States Patent Specification No U.S. Pat. No. 5,650,124 is known the pipette in which for the adjustment of the aspirated liquid volume as the driving member of the plunger working stroke adjustment mechanism a knob is applied, whereas this knob can be moved axially in the handle. When the knob is moved downward into the interior of the handle, the knob enters a seat in the handle and due to friction forces acting the torque indispensable to turn the knob and thereby to re-adjust the volume in the pipette is large. In this manner, the same structure element, that is the knob of the driving member of the plunger working stroke adjustment mechanism, simultaneously is a lock member of the lock mechanism which locks the adjustment mechanism of the plunger working stroke. When the knob is withdrawn from the handle, the braking torque exerted onto the plunger working stroke adjustment mechanism decreases, which enables easy re-adjustment of the volume setting. However, in this pipette with the friction brake of the volume setting, inadvertent re-adjustment of the volume setting is possible, because the knob, during locking the volume setting in course of moving the knob downward into the seat in the handle, can simultaneously realize a rotational motion and a sliding motion in relation to the handle, whereas the rotational motion of the knob results in the change of the aspirated liquid volume setting. Moreover, in this pipette, the lock mechanism, which locks the plunger working stroke adjustment mechanism, is the releasable friction brake between the driving member of the adjustment mechanism and a wall of the handle. Thus, any dimensional inaccuracies of the handle or disadvantageous variations in the handle dimensions, which arisen in consequence of autoclaving, results in disadvantageous changes of the value of the braking torque which is exerted in this friction brake onto the adjustment mechanism of the plunger working stroke.
From the patent specification U.S. Pat. No. 5,849,248 is also known the pipette, in which changes in the setting of the aspirated liquid volume are realized by a rotation of the pipetting push button in two directions, whereas the pipetting push button is the driving member of the plunger working stroke adjustment mechanism. While, as the lock mechanism locking the plunger working stroke adjustment mechanism is applied the friction brake which is actuated and releasable by means of an additional knob in the upper part of the handle below the pipetting push button and is movable between LOCKED POSITION and UNLOCKED POSITION of the plunger working stroke adjustment mechanism. This friction brake acts directly onto an adjustment screw of the plunger working stroke producing the braking torque between the adjustment screw and a wall of the handle by respectively formed structure elements of the lock mechanism. In this pipette, the volume is reset only by rotation of the pipetting push button in two direction, whereas due to the adjustment function of the pipetting push button and simultaneous close relative location of the pipetting push button being the driving member of the adjustment mechanism and the knob of the lock mechanism connected with its lock member, in course of actuation or releasing the friction brake by turning the knob of the lock mechanism locking the plunger working stroke adjustment mechanism between LOCKED POSITION and UNLOCKED POSITION, the accidental change of the setting of the aspirated liquid volume by unintentional rotation of the pipetting push button can take place. Moreover, the location of the lock mechanism knob on the upper wall of the handle and below the pipetting push button also creates in course of pipetting in PIPETTING MODE a danger of an inadvertent release of the friction brake from LOCKED POSITION of the plunger working stroke adjustment mechanism by accidental turn of the lock mechanism knob. Further, this pipette requires to be operated with two hands. Firstly, because of the structure of the lock mechanism. Secondly, the operating with the pipetting push button which performs two functions, namely turning with the pipetting push button when it realizes the function of the driving member of the adjustment mechanism and pushing down the pipetting push button as the element of the drawing up and discharging mechanism into the handle during pipetting for expelling the aspirated liquid from the tip, by means of one hand is also uncomfortable.
In turn, from the application specification US 2004/0035228 is known the pipette, in which, instead of the friction brake, as the lock mechanism locking the plunger working stroke adjustment mechanism is applied a coupling which decouples the pipetting push button, being simultaneously the driving member knob of the plunger working stroke adjustment mechanism, from the adjustment screw of the plunger working stroke. In the effect, after the actuation of the coupling, it is possible in ADJUSTMENT MODE to adjust easily the desired volume value of the liquid and that is both by means of the pipetting push button and by means of the knob inside the handle, which knob constitutes after the coupling actuation another driving member of the plunger working stroke adjustment mechanism and which simultaneously serves for disengagement/engagement of the coupling between LOCKED and UNLOCKED POSITIONS of the plunger working stroke adjustment mechanism. After disengagement of the coupling, that is after moving, inside the handle, the knob as the driving member of the adjustment mechanism to LOCKED POSITION of the plunger working stroke adjustment mechanism, turning with the pipetting push button as well as turning with the knob inside the handle does not cause the adjustment screw of the plunger working stroke to rotation and thereby does not change the preset volume of the aspirated liquid. In LOCKED POSITION of the plunger working stroke adjustment mechanism, the adjustment mechanism, which are situated in different locations in the pipette handle to increase operational comfort of the pipette due to its convenient one-hand operation.
The aimed objects have been achieved in the pipette with the adjustable volume of the aspirated liquid according to the present invention the essence of which is presented below.
A pipette with an adjustable volume of an aspirated liquid, according to the present invention, is built of a handle and of a nozzle and of coupled with them                an exchangeable pipette tip ejection mechanism comprising an ejector push button seated in the upper part of the pipette handle and the ejector seated with its lower end onto the pipette nozzle,        an drawing up and discharging mechanism comprising a pipetting push button connected via a pipetting rod with a piston assembly of which a plunger is placed in the pipette nozzle,        a plunger working stroke adjustment mechanism provided with a drive assembly of an adjustment screw of a plunger working stroke with at least one driving member,        a manually actuated lock mechanism to lock said plunger working stroke adjustment mechanism,        an engaging mechanism to engage said plunger working stroke adjustment mechanism with a counter for indication the volume of the liquid aspirated by the pipette depending on the set plunger working stroke,        a calibration mechanism to change a pipette calibration coefficient determining a relationship between a plunger movement length, which is set by said plunger working stroke adjustment mechanism, and the liquid volume indicated in said counter, whereas said driving member of said drive assembly of said adjustment screw of the plunger working stroke is accessible from outside through at least one window in a wall of the handle, wherein in the pipettesaid lock mechanism locking said plunger working stroke adjustment mechanism comprises a lock member which is non-rotationally mounted relative to said pipette handle and is axially slidable between LOCKED POSITION and UNLOCKED POSITION of the plunger working stroke adjustment mechanism, whereas said driving member of said drive assembly of said adjustment screw of the plunger working stroke is fixed axially and mounted rotationally relative to the pipette handle.        
Preferably, said driving member of said drive assembly of said adjustment screw of the plunger working stroke is via said pipetting rod coupled immovably in the rotation direction with said pipetting push button of said drawing up and discharging mechanism.
Preferably, said lock member is mounted slidably in the axial direction onto said driving member of said drive assembly of said adjustment screw of the plunger working stroke and mounted non-rotationally in said pipette handle.
Preferably, said lock mechanism locking said plunger working stroke adjustment mechanism is a friction brake between said lock member and said driving member, whereas said lock member has a frictional surface on an inner cone and said driving member has a frictional surface on an outer cone.
Preferably, angles of said inner and outer cones of said frictional surfaces are equal.
Preferably, said lock member is a braking the sleeve.
Preferably, said lock member is provided with an elastic braking element of the axial movement of said lock member in said pipette handle in UNLOCKED POSITION of said plunger working stroke adjustment mechanism.
Preferably, said driving member of said drive assembly of said adjustment screw of the plunger working stroke is fixed in axial direction relative to said pipette handle by an interlock which is releasable from said driving member for its displacement in axial direction during the pipette disassembly.
Preferably, said lock member has an outer surface which facilitates a grip.
The advantage of the pipette, following the invention, is that in the pipette is applied the lock mechanism locking the plunger working stroke adjustment mechanism and provided with the additional lock member, different than the driving member of the plunger working stroke adjustment mechanism or than the pipetting push button of the drawing up and discharging mechanism, whereas the operation of the lock member enables easy and quick changing over the pipette from ADJUSTMENT MODE to PIPETTING MODE after the adjustment of the aspirated liquid, volume but simultaneously guarantees the reliability and repeatability of the chosen volume setting both in course of the operation mode change into the one chosen from CALIBRATION, PIPETTING and ADJUSTMENT MODES and in course of the primary operation mode of the pipette that is PIPETTING MODE.
In the present pipette, the lock member of the lock mechanism locking the working stroke adjustment mechanism locks directly the driving member of the adjustment mechanism irrespective of their location relative to the pipette handle, whereas the lock member does not have the possibility to rotate relative to the driving member of the adjustment mechanism and can move only axially relative to the handle. Due to this, the setting of the aspirated liquid volume is secured against accidental modification both in course of the operation mode change into the one chosen from CALIBRATION, PIPETTING and ADJUSTMENT pipette is in PIPETTING MODE. In this pipette, due to the structure of the plunger working stroke adjustment mechanism and the lock mechanism locking this adjustment mechanism, the adjustment of the volume setting of the drawn-up liquid is discrete, and while engaging or disengaging the coupling misadjustment of the desired volume value of the drawn-up liquid can take place. This is because the knob inside the handle is the driving member of the plunger working stroke adjustment mechanism and simultaneously is the lock member of the lock mechanism and as the lock member of the lock mechanism blocks the setting of the liquid volume by disengaging from the adjustment screw of the plunger working stroke and from the counter.
In the pipettes known from the above cited patent specification U.S. Pat. No. 5,650,124 and patent application specification US 2004/0035228,for actuation/release of the lock mechanism locking the plunger working stroke adjustment mechanism is applied the same knob which is also the driving member of the plunger working stroke adjustment mechanism and which serves to set the desired volume value of the drawn-up liquid. It can cause inadvertent resetting of the liquid volume in the moment of actuation/release of the lock mechanism because at the axial motion the knob can simultaneously performs the rotational motion resulting in resetting the previously chosen liquid volume.